The present invention relates to a copier, facsimile apparatus, printer or similar recording apparatus and, more particularly, to a recording apparatus having a finisher capable of binding a stack of sheets at the center of the stack.
Sheets, e.g., paper sheets undergone recording at a recording apparatus are usually punched, stapled, provided with a cover, pasted, marbled, folded, stamped or otherwise finished. Traditionally, such a finishing procedure has been implemented by hand or an on-line automatic machine. Today, a finisher is available which is directly connectable to a recording apparatus to finish a paper stack efficiently.
A stapler, which is a specific form of the finisher, is capable of binding a paper stack at one or more points adjacent to an edge of the stack, binding it at the center, or binding it at the center and folding it at the center like a magazine. Binding and folding a sheet stack at the center is often used since it can readily bind a relatively small number of papers and, in addition, provides the bound papers with an attractive appearance as a book. However, a finisher with such a center binding and center folding capability has rarely been directly connected to a recording apparatus for the following reasons. To begin with, the order of pages carrying images thereon is complicated. Regarding the number of kinds, the center binding and center folding procedure is not sufficient alone. It is likely that the stapler is greater in size than the recording apparatus, obstructing the free use of space pages. Should the stapler be miniaturized, the position for the operator to take out a bound stack would be too low to promote easy operation.
Digital recording, which is a recent achievement in the imaging art, allows image data to be written to and read out of a multipage memory, promoting easy control of pages. Japanese Patent Laid-Open Publication No. 262772/1985, for example, discloses a finisher which folds a paper undergone recording, unfolds it, sequentially stacks such papers in the form of a saddle, and then binds them at the center. Japanese Patent Laid-Open Publication No. 52154/1988 teaches a finisher capable of displaying the order of documents to be copied and how to set a document on a glass platen in a center bind and fold mode. Japanese Patent Laid-Open Publication No. 12513/1987 proposes a finisher of the type determining whether or not to fold a paper stack depending on the paper size. Japanese Patent Laid-Open Publication No. 117174/1989 teaches a finisher having a stop for folding which moves in matching relation to size data representative of an irregular paper size entered. Further, Japanese Patent Laid-Open Publication No. 32271/1989 discloses a finisher which binds a paper stack, measures the size of the papers to determine a folding position, and then automatically adjusts the position of a stop on the basis of the resulting data. Specifically, this finisher determines a folding length in terms of an interval between the time when the trailing edge of a paper stack moves away from a sensor on a first path and the time when the leading edge of the stack reaches a sensor on a second path.
A folder for folding a stack of recorded papers has been proposed and realized in various forms in the past. The prerequisite with a folder is that a folded stack be provided with accurate dimensions, i.e., it be folded at an accurate position. The folding position depends on the physical property of papers. For example, as a paper stack abuts against a stop, it is caused to bend at the intermediate portion thereof and then caught by a pair of fold rollers to be fully folded. The distance between the leading edge of the paper stack and the folding position depends on the elasticity of papers. During the interval between the time when the paper stack abuts against the stop and the time when it is further driven and caught by the fold rollers, the papers of the stack undergo some elastic deformation between the stop and the fold rollers. This deformation and the bending rate of the folded portion depend on the papers. As a result, the folding position differs from one kind of paper to another even when the stop is held in the same position. In light of this, it has been customary for a skilled operator to finely adjust, for example, the position of the stop by repeating tentative folding. This, however, wastes time, labor, and cost. Furthermore, it is difficult to combine the center folding and binding function with the edge binding function. In addition, when a great number of papers should be folded, it is a common practice to sense the innermost paper at the trailing end and the outermost paper at the leading end. This makes the measurement inaccurate, e.g., the measured value depends on the number of papers.
A binder with a center binding and folding capability has a binding function. Hence, it is preferable to use such a binder for edge binding also.